Solar reflectivity has gained large prominence as a roofing feature due to regulatory pressure and customer preference. Traditionally, to produce solar reflective (SR) granules, standard base rock is crushed to a particle size of about 0.5 mm to 1.5 mm and the sized particles are coated to cover the granules with a solar reflective layer. The SR coating of the granules contributes to a significant amount of the material, energy, time, and total costs of producing the SR granules. Moreover, when crushing the base rock, about 40 wt % to 50 wt % of the crushed stone is considered as waste material, also called granule fines, since the particle sizes are lower than the desired size range for roofing granules.
There is a need for more economic ways of manufacturing roofing granules with a high solar reflectance. Furthermore, there is a continuing need for roofing granules with a high solar reflectance but low lightness L* value.